Queensland Police have offered a $250,000 reward for information leading to an arrest or conviction in the suspected murder of Queensland schoolgirl Tiahleigh Palmer.

The 12-year-old disappeared from Marsden State High School on October 30. Palmer's remains were found on the banks of Pimpama River in Brisbane's south on November 5.

Authorities believe the 12-year-old had arranged to meet someone after she was last sighted exiting the school at 8:20am.

Regional Crime Coordinator Detective Superintendent Dave Hutchison announced the reward on Monday, claiming authorities have spoken to a number of people who they believe aren't revealing all they know about the case.

“Now for whatever reason, they’re not coming forward with that information – the information that we want. And that might be through fear. It might be through loyalty. It might be through their own involvement in it and they’re afraid themselves of getting into trouble," Detective Superintendent Hutchison said in a press conference on Monday.

“Importantly the offer in addition to the reward also includes a recommendation for an indemnity from prosecution for any accomplice who didn’t actually commit the crime who first comes forward with such information."

Detective Superintendent Hutchison would not confirm Palmer's cause of death or any suspects in the case.